The patent document U.S. Pat. No. 4,079,596 A relates to a heat engine, or a heat pump, in which the working medium used is subjected alternatively to solidification and melting operations. A working medium so used is referred to as an type working medium. In the heat engine, an S/L type working medium is subject to cyclic operations, each cycle comprises a high temperature melting step conducted under a first pressure, and a low temperature solidification step conducted under a second pressure. In the heat pump, each cycle comprises a high temperature solidification step conducted under a first pressure and a low temperature melting step conducted under a second pressure. When a non-aqueous medium is used, the first pressure and the second pressure are a relatively high pressure and a relatively low pressure, respectively. When an aqueous medium is used the two pressures are a relatively low pressure and a relatively high pressure, respectively. It is noted that the operation of a heat pump is the reverse operation of a heat engine.
The patent document U.S. Pat. No. 5,263,323 A relates to a thermal actuator, also known as a heat capacitance motor, which derives its energy from the physical expansion of paraffin wax as it changes from solid to liquid when heated within an enclosure such as a cylinder. This energy is converted into mechanical force which causes translation of a piston slidably mounted within the cylinder, thus creating hydrostatic pressure which is converted to work. The thermal actuator may be utilized in various drug delivery systems in which the hydrostatic pressure created by the actuator is used to expel the contents of a syringe.
The patent document GB 1,341,163 A relates to a device for converting thermal energy to mechanical energy, wherein heat is applied to liquid in one or more annular chambers which is/are in communication with, but thermally insulated from, a further annular chamber so as to cause a volume expansion thereof, and hence a movement of an actuating rod attached thereto. The device comprises annular chambers 9, 10, 2, chamber 2 being seated by spring bellows 6. Heating elements 11, 12 vaporize the liquid in chambers 9, 10, thereby causing contraction of the bellows 6 and hence movement of a rod 7. Use of only one of the elements 11, 12 moves the rod 7 by a half-stroke.
The patent document U.S. Pat. No. 4,283,915 A relates to a hydraulic fluid generator. Two sources of water with a temperature differential of say 20° F. flow alternatively through heat exchanger tubes to expand and contract a working liquid that has a high coefficient of thermal expansion, the whole working cycle being carried out below the boiling point of the working liquid. With check valves preventing reverse flow, the expansion and contraction of the working liquid provides a high pressure hydraulic output which may be used to drive a hydraulic motor. To provide substantially steady output flow, four banks of heat exchangers may be operated sequentially with hydraulic accumulator means smoothing out the flow pulsations. Each bank has a four-stage operating cycle and electrical circuitry controls the four banks simultaneously to cause the four different stages to occur in certain of the four different banks in staggered relation for producing a substantially constant overall hydraulic output.
The patent document U.S. Pat. No. 5,375,983 A relates to a system for utilizing the expansion of water as the water is transformed from a liquid state to a solid state includes a rigid outer container and a flexible inner bladder received centrally within the outer container. Hydraulic fluid is received within the bladder, and water is disposed between the bladder and outer container. The hydraulic fluid is pressurized as the water is lowered in temperature to a freezing temperature. The pressurized fluid may be stored for selective release from the bladder to produce work utilizing the energy of the pressure within the hydraulic fluid.
The patent document WO 89/12748 A1 relates to a process and apparatus for conversion of low value thermal energy into mechanical energy by thermal expansion of an inert liquid expansion medium, which in a relatively low temperature range of not higher than 80° C. has a relatively high expansion coefficient, which medium is contained in pressure tubes included in a regeneration cylinder, which pressure tubes are stepwise heated or cooled by a thermal medium circulating in the cylinder without parts of the thermal medium with different temperatures being intermingled. Examples of the expansion medium are paraffin's.
The above presented documents disclose different solutions within this technical area without presenting art optimal solution regarding thermal efficiency and structural strength. Furthermore, the solutions presented in these documents are not optimal regarding power density, manufacturing efficiency and manufacturing costs.